With the fast increase of radio communication service requirements, spectrum resources available currently are becoming fewer and fewer. Large quantities of spectrum tests, however, prove that the “shortage” of spectrum resources is not a result of the lack of spectrum resources but a result of the insufficient utilization of the spectrum resources caused by the current fixed spectrum management policy. Cognitive radio (Cognitive Radio, CR hereinafter) can sense the radio communication environment, dynamically detect and efficiently utilize idle spectrum resources, and allow a secondary user to have multidimensional spectrum reuse with a primary user in time, frequency, and space. This greatly relieves the constraint of spectrum and bandwidth restriction on the development of radio technologies. This technology is believed to be one of the hottest radio technologies in the future.
Spectrum sensing is a key technology of cognitive radio. The purpose of spectrum sensing is to monitor and detect activities of the primary user signals in a specific frequency band: When an idle spectrum is detected, the cognitive radio system can use the frequency band; and when a primary user signal is detected, the cognitive radio system must exit the frequency band in a specified duration. The performance of spectrum sensing mainly depends on the following factors:
Sensing threshold: it is the minimum primary user signal strength that a sensor node needs to detect. If, at a frequency, the sensor node detects that the primary user signal strength exceeds the sensing threshold, it can be considered that the primary user appears at the frequency; otherwise, it can be determined that the frequency is idle and can be used.
Primary user protection time: it is the maximum interference time allowed for the primary user, which is the time from when the primary user appears to when the secondary system is detected and exits the frequency.
Sensing performance: it includes detection probability and false alarm probability, where, when the detection probability is higher, the protection for the primary user is better and when the false alarm probability is lower, the service continuity of the secondary system is more benefited.
In the prior art, the sensing threshold determining method is to calculate the received signal strength at a specific location as the actual sensing threshold in the location by using the transmit power of the primary user and based on a certain channel model.
Conventional channel models are all general channel models specific to a certain landform, where, with regard to a certain landform (such as urban area, suburban area, opening area, and mountain area), as long as the distance to the primary user transmitter is the same, whatever geographic environment the sensor node is located in, the sensor node has the same sensing threshold. This will result in the inconformity between the calculated sensing threshold and the actual sensing threshold. If the sensing threshold is determined based on the conventional method, the sensing threshold may be set too high, so that the detection probability is lower, or the sensing threshold is set too low, so that the sensing overhead is increased and the false alarm probability is higher. Therefore, the conventional sensing threshold determining method has great defects.
When the conventional method is adopted to determine the sensing threshold, it is necessary to learn information, such as the location of the television (Television, TV hereinafter) transmitter and the transmit power, but such information is not available at will in any county and region. If the information is not learned in advance, it is hard to determine the sensing threshold in the location of the sensor node and a uniform low sensing threshold has to be adopted to restrain the behaviors of the sensor node, thereby resulting in a too low sensing threshold.